Inhibition of transglutaminase 2 mitigates transcriptional dysregulation in models of Huntington disease

Abstract

Caused by a polyglutamine expansion in the huntingtin protein, Huntington's disease leads to striatal degeneration via the transcriptional dysregulation of a number of genes, including those involved in mitochondrial biogenesis. Here we show that transglutaminase 2, which is upregulated in HD, exacerbates transcriptional dysregulation by acting as a selective corepressor of nuclear genes; transglutaminase 2 interacts directly with histone H3 in the nucleus. In a cellular model of HD, transglutaminase inhibition de-repressed two established regulators of mitochondrial function, PGC-1α and cytochrome c and reversed susceptibility of human HD cells to the mitochondrial toxin, 3-nitroproprionic acid; however, protection mediated by transglutaminase inhibition was not associated with improved mitochondrial bioenergetics. A gene microarray analysis indicated that transglutaminase inhibition normalized expression of not only mitochondrial genes but also 40% of genes that are dysregulated in HD striatal neurons, including chaperone and histone genes. Moreover, transglutaminase inhibition attenuated degeneration in a Drosophila model of HD and protected mouse HD striatal neurons from excitotoxicity. Altogether these findings demonstrate that selective TG inhibition broadly corrects transcriptional dysregulation in HD and defines a novel HDAC-independent epigenetic strategy for treating neurodegeneration.

Real-time kinetic method to monitor isopeptidase activity of transglutaminase 2 on protein substrate

“…Approximately 0.3 µM ZDON was enough for complete inhibition of the isopeptidase activity which is in a good correlation with the expected value in case of an irreversible inhibitor in the presence of 0.3 µM TG2 although the apparent IC50 value was 30.7 nM (calculated by fitting a dose-response curve hypothesising standard slope) which is lower than a reported one in an in vitro transamidation assay [24].…”

“…However, the effects of newly developed inhibitors were always tested on the crosslinking activity of TG2 and there has been no comparison of their effect on isopeptidase activity of TG2, particularly in a kinetic, protein substrate assay that has not existed so far. A commercially available, cell permeable, irreversible active site directed inhibitor of TG2, the ZDON (Zedira, [24]) was tested in our newly developed method (Fig. 2C).…”

Transglutaminase is a Therapeutic Target for Oxidative Stress, Excitotoxicity and Stroke: A new Epigenetic Kid on the Cns Block

“…We have recently shown that these enzymes also modulate transcription. 5 Inhibition of their activity leads to normalization of genes repressed in neurodegenerative conditions and subsequently neuroprotection. There is an increase in TG transamidating activity in different models of stroke [6][7][8][9] and inhibition of TG with an FDA approved, nonselective inhibitor, cystamine, showed beneficial effects.…”

“…Accordingly, TG2 is upregulated in cerebellar granule cells exposed to NMDA toxicity 64 and its inhibition in medium-sized spiny neurons derived from HD mice (YAC128) or wild-type controls is sufficient to protect neurons from NMDA-mediated toxicity. 5 A putative mechanism by which the inhibition of TG activity halts excitotoxic death could involve the derepression of peroxisome proliferator-activated receptor-g coactivator-1d expression. 5 Indeed, it has been recently reported that peroxisome proliferator-activated receptor-g coactivator-1d blocks extrasynaptic NMDA receptor activity and excitotoxicity in models of HD.…”

“…5 A putative mechanism by which the inhibition of TG activity halts excitotoxic death could involve the derepression of peroxisome proliferator-activated receptor-g coactivator-1d expression. 5 Indeed, it has been recently reported that peroxisome proliferator-activated receptor-g coactivator-1d blocks extrasynaptic NMDA receptor activity and excitotoxicity in models of HD. 65 …”